Put the dried wild mushrooms in a heatproof bowl and pour 400ml (14fl oz) of boiling water over to cover. Set aside for 20 minutes, until they have plumped up. Drain the mushrooms and gently squeeze dry, reserving the soaking liquid.
Heat a large pan and add the oil. Add the chestnuts, the onion and drained wild mushrooms and sweat gently for 10 minutes, until golden brown, stirring occasionally. Season to taste.
Add the thyme to the pan with the reserved soaking liquid, madeira wine and the stock, stirring to combine. Bring to the boil, then reduce the heat and simmer for another 20 minutes. Stir in the cream and allow to heat through for 1 minute, then whizz with a hand-held blender until as smooth as possible.
Season to taste, then blend again until light and foamy, tilting the pan to get the maximum effect.
To serve, ladle the soup into warmed bowls. Garnish each one with the chives and micro herbs.